[Wien] Constraining position in case.inM

Laurence Marks laurence.marks at gmail.com
Sat Mar 27 08:28:27 CET 2021


Also read as it might be relevant
http://www.wien2k.at/reg_user/textbooks/README_Constraints.pdf

In simple cases these work well, although they are experimental.

Caveat: normally fixing atomic positions is poor science.
_____
Professor Laurence Marks
"Research is to see what everybody else has seen, and to think what nobody
else has thought", Albert Szent-Györgyi
www.numis.northwestern.edu

On Sat, Mar 27, 2021, 02:09 Peter Blaha <pblaha at theochem.tuwien.ac.at>
wrote:

> > I have another query;
> >
> > If I want to vary only x coordinate while maintaining y & Z coordinate
> > to the same value of x, what should I do?
> >
> > As an example in the desired structure, I want to have (x, x,x) & want
> > to vary the only x, what should be the process?
>
> This depends on your structure and symmetry. Most likely, the position
> (x,x,x) is "fixed" by symmetry to have 3 equal values. You can see this
> eg. from your forces, that this atom has only ONE force component (LM=1
> 0) and a local rotation matrix putting the z-axis into 111 direction.
>
> In such a case you have to break symmetry. This means: in a new
> directory, change (x,x,x) manually to (x,y,y) (and similary to
> equivalent atoms if Mult gt.1). Then do    init_lapw.
> (It could be that positions become inequivalent by this procedure and
> you will get more non-equivalent atoms).
> Then check your symmetry (eg. in case.outputs, if the position has a
> symmetry such that y and z must be identical, or if they can move freely
> (check eg. the LM-list in case.outputs: if they include 3 L=1 terms,
> they are independent, if they have only 2 L=1 values, they are fixed to
> be identical.
>
> This will allow to manipulate x and y,y (or y,z) individually.
> >
> > with regards,
> >
> >
> >
> > On Sat, 27 Mar 2021 at 12:15, Peter Blaha <pblaha at theochem.tuwien.ac.at
> > <mailto:pblaha at theochem.tuwien.ac.at>> wrote:
> >
> >     Basically the steps are correct.
> >
> >     Only for step (4): if min_lapw works well for your case, you may
> >     continue. However, remember that the recommended way to optimize
> >     positions is now:
> >     run_lapw -min
> >
> >     Regards
> >
> >     Am 27.03.2021 um 06:47 schrieb shamik chakrabarti:
> >      > Dear Wien2k users,
> >      >
> >      >                            If I want to keep some positions of
> >     atoms of
> >      > a primitive cell during force minimization should I follow the
> >     following
> >      > steps;
> >      > (1) put 0 by replacing 1 for the atoms (for all the coordinates
> >     x, y, z)
> >      > which I want to remain fixed in case.inM
> >      > (2) remove file case.tmpM
> >      > (3) x pairhess
> >      > (4) min_lapw
> >      >
> >      > Looking forward to your reply in this regard.
> >      >
> >      > with regards,
> >      > --
> >      > Dr. Shamik Chakrabarti
> >      > Research Fellow
> >      > Department of Physics
> >      > Indian Institute of Technology Patna
> >      > Bihta-801103
> >      > Patna
> >      > Bihar, India
> >      >
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> >
>  --------------------------------------------------------------------------
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> >     Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
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> >
> >
> >
> > --
> > Dr. Shamik Chakrabarti
> > Research Fellow
> > Department of Physics
> > Indian Institute of Technology Patna
> > Bihta-801103
> > Patna
> > Bihar, India
> >
> > _______________________________________________
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> --
> --------------------------------------------------------------------------
> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
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